Field of the Invention
The present invention relates to a Wireless Distribution System, more specifically, to an improved access point and an improved method of controlling channel change in the access point for the Wireless Distribution System.
Description of the Related Art
A Wireless Distribution System (WDS) is a system enabling wireless connection either between access points or between an access point and a repeater on the basis of technology that expands a wireless service area which is hardly covered by using one access point without adding an extra wired line. A wireless data transmission method in a WDS section is defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard.
In order to establish a WDS link, two (2) access points in a WDS must have a counterpart's Media Access Control (MAC) address information and must wirelessly transmit and receive data in a same channel. When these two (2) access points have a counterpart's MAC address, they operate as if a new bridge port was created.
Data in a WDS section is defined in the IEEE 802.11 standard to be distinguished from general data transmitted between an access point and a terminal. The WDS section data uses all of four (4) addresses in an IEEE 802.11 MAC header, and uses 2 bits of ToDS and FromDS among control fields of the MAC header bits and ToDS and FromDS are both set to “1”. The four (4) addresses refer to RA (Receiver Address), TA (Transmitter Address), SA (source address), DA (destination address). Data between an access point and a terminal, however, uses a maximum of three (3) addresses according to frame types and uses the bits of ToDS and FromDS set to (1, 0), (0, 1) or (0, 0). Three (3) addresses refer to DA, SA, BSSID (Basic Service Set Identifier). Clearly, data in a DWS section and data transmitted between an access point and a terminal are different from each other.
To normally transmit and receive data in a WDS section, a counterpart access point's MAC address, a security mode in the WDS section, and a channel must be properly set in two (2) access points. The counterpart access point's MAC address and the security mode are hardly changed once they are set. Moreover, since a user manually changes them, they cannot be changed without the user's knowledge. The channel, however, may be changed without a user's knowledge when the user uses an automatic channel other than a fixed channel, and thus a WDS link may be disconnected.
Particularly in an 11a (5 GHz) band, many countries indispensably require supporting of a Dynamic Frequency Selection (DFS) function. When the DFS function is supported, the channel of an access point may be changed to avoid the surrounding radar signal interference. When a WDS is used in the 11a band under this situation, channels of two (2) access points may be set differently, and it may be impossible to normally support the WDS.